Display screen or portion thereof with a graphical user interface



The FIGURE is a front view of a display screen or portion thereof with a graphical user interface showing our new design.

The broken line at the periphery of the FIGURE illustrates the display screen and the remaining broken lines illustrate portions of the graphical user interface. None of the broken lines form part of the claimed design. 

CLAIM I claim the ornamental design for a display screen or portion thereof with a graphical user interface, as shown and described. 